SFTs under dynamic loads: new design issues and numerical simulation

In the paper some recent developments of the design trends in the field of seabed anchored Submerged Floating Tunnels are reviewed; the focus is on the implications on the anticipated dynamic behavior of the tunnel and on its numerical simulation. The design needs here considered are mainly of two types; the first is the necessity to cope with more stringent fire regulations. The second is the consideration of partial-flooding loading conditions, which was neglected in older designs according to the "no water ingress" principle. Both needs lead to the introduction, in the conceptual design, of the twin-tube solution, where two tunnels run parallel and are interconnected in order to allow fire escape. In addition, partial or total flooding of one of the two is considered, while the other can deliver sufficient buoyancy to avoid collapse. This evolution, along with the recent design activity performed within the E-39 Norwegian project, requires, in the writers' opinion, a review of the fundamental design choices, with a twofold purpose: first, to "classify" available options in view of coping with environmental loading scenarios (seismicity, wind waves, currents, naval and road/rail traffic, etc.) of different severity. Second, to discuss the various design configurations in view of the predictability of their structural behavior, especially under dynamic actions, this being a very delicate aspect for a never-built construction. Within this context, scope of the paper is to address the basic aspect of the SFT conceptual design along with the experimental and/or numerical procedures for simulating the dynamic behavior of the SFT under extreme environmental conditions. An example is finally given, illustrating some typical modelling options in relation to a SFT solution for the Messina Strait crossing, with particular reference to seismic response and seismic-induced hydrodynamic loading.